Impact of eastern dwarf mistletoe (Arceuthobium pusillum) infection on the needles of red spruce (Picea rubens) and white spruce (Picea glauca): oxygen exchange, morphology and composition

Abstract

Eastern dwarf mistletoe (Arceuthobium pusillum Peck) is a hemiparasitic angiosperm that infects white spruce (Picea glauca (Moench) Voss) and red spruce (P. rubens Sarg.) in northeastern North America. The effects of mistletoe infection differ substantially between white and red spruce, with white spruce suffering greater infection-induced mortality. In the present study, we sought to determine the role that species-specific differences in needle-scale responses to parasitism may play in the observed differences in the effect of infection on host tree health. Based on the measurements made, the most apparent effect of parasitism was a reduction in needle size distal to infections. The magnitude of this reduction was greater in white spruce than in red spruce. Eastern dwarf mistletoe was a sink for host photosynthate in red spruce and white spruce; however, there were no adjustments in needle photosynthetic capacities in either host to accommodate the added sink demands of the parasite. Needle total nonstructural carbohydrate concentrations (TNC) were also unaltered by infection. Red spruce needles had higher TNC concentrations despite having lower overall photosynthetic capacities, suggesting that red spruce may be more sink limited and therefore better able to satisfy the added sink demands of parasitic infection. However, if carbon availability limits the growth of the mistletoe, one may expect that the extent of the parasitic infection would be greater in red spruce. Yet in the field, the extent of infection is generally greater in white spruce. Taken together, these results suggest that dwarf mistletoe may not substantially perturb the carbon balance of either host spruce species and that species-specific differences in needle-scale responses to the parasite cannot explain the contrasting effects of infection on white spruce and red spruce.

Impact of White Mistletoe (Viscum album ssp. abietis) Infection on Needles and Crown Morphology of Silver Fir (Abies alba Mill.)

“…On the other hand, according to Ehleringer et al (1985), Marshall and Ehleringer (1990), Escher et al (2004) xylem parasites and in particular mistletoe species are highly dependent on the supply of organic carbon and nitrogen from their hosts, shrinking the leaf area. Reduction in needle size could be a response to mistletoe infection, because smaller needles would require lower amounts of nitrogen and fixed carbon (Reblin et al, 2006).…”

“…This is in line with the results of Rigling et al (2010) for pine mistletoe (Viscum album ssp. austriacum) and Reblin et al (2006) for dwarf mistletoe (Arceuthobium pusillum).…”

“…Furthermore any severe infection is frequently associated with premature dieback of host trees (Mathiasen et al, 2008;Peter -Contesse, 1937;Plagnat, 1950). As growth of the infected trees was subject to several previous studies Nanu, 1969;Noetzli et al, 2003), it is of interest whether white mistletoe infection is responsible for crown degradation of silver fir, since other genera of mistletoes, such as Archeutobium, seems to be responsible for a reduction of host's needle size (Logan et al, 2002;Reblin et al, 2006).…”

Mistletoes: Pathology, Systematics, Ecology, and Management

“…5C), alter host phytohormone balance, resulting in the formation of dense masses of branches called witches'-brooms (126,159,187). Branches from witches'-brooms exhibit features atypical of uninfected host tissue such as: increased longevity (222); elimination or reduction of seed and cone production (24,116); increased branch elongation on some hosts (83,209); increased biomass compared with uninfected branches of the same age (209); and decreased number, length, and mass of needles (28,29,175). While witches'-brooms are the most easily observed symptom of dwarf mistletoe infection and serve as large nutrient sinks that contribute to the decline of host vigor and growth (136), they also appear to have positive effects in an ecological context (see below).…”

Native hemiparasite and light effects on photoprotection and photodamage in a native host

“…In contrast, Shen, Prider et al (2010) found that Chl a/b ratio of C. scoparius stems increased in response to infection with C. pubescens under ambient light. Most other studies have reported no effect of parasitism on host Chl a/b ratio (Cechin and Press 1994;Hibberd, Quick et al 1996;Jeschke, Baig et al 1997;Logan, Huhn et al 2002;Reblin, Logan et al 2006;Cameron, Geniez et al 2008;Shen, Hong et al 2011;Shen, Xu et al 2013). In our study, both Chl a and Chl b declined to a similar degree in the infected plants in HL, whereas in LL, there was a strong decrease in …”